In wireless communication systems in which portable or mobile communication devices communicate with a base station or access point, such as a CDMA2000, GSM and WLAN communication system, the mobile communication device is typically a hand-held device, such as a cellular telephone, for example. The communication devices are provided with wireless data and/or voice services and can connect devices such as, for example, laptop computers, personal data assistants (PDAs), cellular telephones or the like through the base station or access point to a network.
Each communication device is equipped with an antenna. In some antenna embodiments, the antenna protrudes from the housing or enclosure of the communication device to improve antenna performance by adequately separating it from the electronic components carried by the housing. The protruding antenna may be a monopole or dipole antenna, for example.
Another type of antenna used with communication devices is a switched beam antenna. A switched beam antenna system generates a plurality of antenna beams including an omni-directional antenna beam and one or more directional antenna beams. Directional antenna beams provide higher antenna gains for advantageously increasing the communications range between the base station and the communication device, and for also increasing network throughput. A switched beam antenna is also known as a smart antenna or an adaptive antenna array.
U.S. Pat. No. 6,876,331 discloses a smart antenna for a mobile communication device. This patent is assigned to the current assignee of the present invention, and is incorporated herein by reference in its entirety. In particular, the smart antenna includes an active antenna element and a plurality of passive antenna elements protruding from the housing of the mobile communication device.
The physical length of an antenna, including the length of the active and passive antenna elements, is normally a minimum of a quarter wavelength of the operating frequency. Cellular telephones commonly operate in the 1.9 GHz range, which corresponds to an antenna length of about 1.6 inches. Protrusion of the various types of antennas from the housing of a cellular telephone may be broken or damaged when carried by a user. Even minor damage to a protruding antenna can significantly change its operating characteristics. In addition, lengthy protrusions take away from the appearance of a cellular telephone. Even for fixed devices, such as access points, protruding antennas can restrict their placement because of physical or esthetic reasons.
One approach to this problem is to have an antenna that is pulled out or extended by the user when in use. When not in use, the antenna is recessed within the mobile communication device. There are several problems with this approach. First, the user needs to extend the antenna for best performance, which is not always done. If the antenna is pulled out with excessive force, this may also lead to breakage, as well as if the user holds the mobile communication device by the extended antenna. For multi-frequency communication devices (e.g., 800 MHz and 1.9 GHz), the optimum length of the antenna varies depending on the operating frequency.
Another approach for an external antenna that is not easily damaged is based upon generation of an ionized air stream, i.e., a plasma antenna. U.S. Pat. No. 6,674,970 discloses a plasma antenna that includes a laser that emits a laser beam from an output aperture that travels along a vertical axis into the atmosphere. The laser beam interacts with a medium above it to form an unbounded plasma column. The plasma column comprises ions and electrons that produce an upward current in response to an abrupt ionization of the air in the column. A drawback of the '970 patent is that the ionized air needs to be in an enclosure, and requires generation equipment beyond what would be practical in a mobile communication device, such as a cellular telephone.